In spite of Google Chrome's sandboxing feature, which allows
each tab and process to run in a separate thread to prevent the browser
from fully crashing if a plug-in or bad bit of Web site code causes
issues, the entire browser crashed, losing any unsaved work at the same
time.

Google engineer Tim Steele took to the firm's developer forums to confirm
that, in spite of the apparent link between Gmail's outage and Chrome
crashes, it was Google Sync that was causing the browser to crash
worldwide, which ultimately then had a knock-on effect to other Google
services, not limited to Gmail, Google Docs, Drive and Apps.

Google Sync keeps a user's Chrome browser in sync when they log in to
their browser. Bookmarks, extensions, apps and settings are transferred
across to the new Chrome browser on another machine when a user logs
in.

But this back-end service's failure had a knock-on effect to Chrome
browsers. (Presumably, browsers that aren't set up to synchronize
settings were not affected). Steele noted that
Google's Sync Server relies on a component to enforce quotas on
per-datatype sync traffic, which failed. The quota service "experienced
traffic problems today due to a faulty load balancing configuration
change."

He added: "That change was to a core piece of infrastructure that
many services at Google depend on. This means other services may have
been affected at the same time, leading to the confounding original
title of this bug."

As a result, Google's Sync Server "reacted too conservatively" by
telling the Chrome browser to "throttle 'all' data types," without
taking into account for the fact that the browser doesn't support all
these data types. This caused Chrome to crash en masse around the world.

The 'too-long, didn't-read' version is that Google changed
something, it didn't work, and it caused the crashes. No hackers were
involved, and the outage and crashes certainly were not a result of a
denial-of-service attack.